When the truth emerges, it has to be squashed. Lord Malloch-Brown, who is standing down as a Foreign Office minister this week, was forced yesterday to correct an interview he gave to the Daily Telegraph, in which he said British troops did not have enough helicopters. This is what every British general had been telling government for years. But what if there were enough helicopters? What does it say about the control Britain claims to have over Afghan territory eight years on, if the only safe way troops can move around is by air? And what if the cash-rich Taliban got their hands on surface-to-air missiles, as the mujahideen did before them? It would make communications with all forward operating bases vulnerable. Pull on one thread and the carpet unravels.

Now look at the military situation through the enemy's eyes. Two major thrusts by US and British troops into territory the Taliban once dominated have resulted in record US and Isaf casualties: 31 US troops and 20 Isaf, 18 of them British, have been killed so far this month and many more grievously injured. The Taliban have lost men, but they have an endless supply of recruits. And they would be even less bothered by loss of territory. The battlefield has merely grown. History tells them to be patient. It tells them that they will return to the lands from which they have been ousted. Confronted by large numbers of foreign troops, Taliban commanders could rationally conclude they are weathering the storm. They buy what weapons they need with cash – guns, explosives, and Pashtun villagers to plant them – and their most effective weapon is a low-tech one, the improvised explosive device. Their war effort is eminently sustainable. Ours is not.

It becomes even less so when you examine the blithe assumptions Barack Obama's commanders are making. Rory Stewart demolished them in the London Review of Books, but others just as knowledgable of the terrain, such as the CIA former station chief in Kabul, have as well. Assumption number one: that coalition forces can build an effective, centralised Afghan state in the space liberated by their troops. Such a state has never existed in recent memory. Assumption number two: that the counter-insurgency tactics that worked in Iraq will work again in Afghanistan. Why so? Afghan tribal chiefs bear little relation to the Iraqi Sunni tribal leaders who turned against al-Qaida. They lack coherence or any political programme. Assumption number three: that south Helmand is the frontline of a global war. The masterminds of the 7 July attacks on London in 2005 were trained in Pakistan's Federally Administered Tribal Areas, not Afghanistan. And if every failed state has to be occupied to prevent squatters, is this not a recipe for invading Yemen, Somalia, or anywhere along the conveniently named crescent of crisis?

The empty rhetoric has to stop. State-building from the ramp of a Chinook is a fantasy, a folie de grandeur. The war against militants will not be won by expanding the battle-space. The resolution to this "good war'' will not come from Kabul alone, but will be dependent on every neighbouring country with a stake in the conflict. The directorate for Inter-Services Intelligence made a telling point to the New York Times yesterday when it warned that a push by US marines in southern Afghanistan would force militants into Baluchistan. We have to stop thinking of Helmand as the frontline in a war that ends on the streets of London or Manhattan, and start thinking of what the growing conflagration is doing to Afghanistan's immediate neighbourhood. There are no good options after eight years of warfare, only least worst ones. We should stop pouring more oil on to this fire and start thinking of realistic outcomes. And we should be doing this now.

• This article was amended on Friday 24 July. A reference to a serious criminal case was removed.